Round up (4)
'round up' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for muster that I've seen before include "Assemble for duty" , "Mobilize" , "Assemble, gather together" , "marshal" , "Gather or bring together" .)
'round up' is the definition.
(as in herding or rounding up sheep)
This is the entire clue.
(Other definitions for herd that I've seen before include "Collection of cattle" , "Stock of cattle" , "Crowd of cattle" , "Group of animals of one kind" , "Group of cows, elephants etc" .)